It is known that various metal values, particularly copper and nickel values can be extracted from aqueous leach solutions with oximes. Basically, this prior art procedure includes the steps of contacting the metal containing aqueous solution with a water immiscible organic phase containing the oxime. By allowing the oxime in the organic phase to contact the metal values in the aqueous phase through mixing, metal values are extracted from the aqueous phase onto the oxime in the organic phase. The loaded organic phase is easily separated from the aqueous solution by virtue of the immiscibility of the two phases. Once the organic phase is separated from the aqueous phase, the metal values can be stripped from the loaded oxime by contacting the oxime with a stripping agent. The stripped metals then can be reduced to their elemental form by a variety of reduction procedures including electrowinning. Patents directed to oximes which are representative of the prior art include U.S. Pat. No. 3,224,873 to Swanson entitled "Liquid-Liquid Recovery of Copper Values Using .alpha.-Hydroxy Oximes"; U.S. Pat. No. 3,592,775 to Swanson entitled "Compositions Containing Phenolic Oximes and Certain .alpha.-Hydroxy Aliphatic Oximes"; and U.S. Pat. No. 3,276,863 to Drobnick entitled "Separation of Nickel and Cobalt Values Using .alpha.-Hydroxy Oximes". U.S. Pat. No. 3,197,274 to White entitled "Liquid-Liquid Recovery of Metal Values Using Hydroxyamine Extractants" discloses similar technology; but the extractant disclosed therein is an amine.
Factors to be considered in the selection of an ion exchanger such as an oxime include loading capacity, tendency to form emulsions (particularly at high pH's), extraction kinetics, stripping rate, and phase separation rates.